Remove LOCK_KEEP and READ_CHECK_EXISTENCE from vgsplit.

Remove LOCK_KEEP and READ_CHECK_EXISTENCE from vgsplit.

Remove LOCK_KEEP and READ_CHECK_EXISTENCE from vgsplit.
These flags are no longer necessary.  We now check for existence
in a differnet function, and it is not necessary to keep the lock.
Removing these flags simplifies the new vg_read() interface.
After this patch, we can fully remove LOCK_KEEP.
READ_CHECK_EXISTENCE needs a bit more work before full removal.

Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>